There seem to be several options for setxkbmap such as -option caps:backspace which makes caps a backspace. However I cannot seem to find an option that makes backspace an escape key. How do I create a single setxkbmap command that changes the backspace key to an escape key?

(where bksp is the name of the symbol file and bksp_escape is the group name that was defined in this file) and add it to the options list in the rules set you're using - assuming evdev - so place it in /usr/share/X11/xkb/rules/evdev under ! option = symbols:

In Gnome 3 you can make the option permanent via dconf (or gsettings in terminal) e.g. add 'bksp:bksp_escape' to the org​>gnome​>desktop​>input-sources​>xkb-options key (note that in dconf values are separated by comma+space).

Finally, note that both evdev and evdev.lst will be overwritten on future upgrades (but not your custom bksp symbol file) so you'll have to edit them again each time the package that owns them is upgraded (on archlinux it's xkeyboard-config). It's easier to write a script that does that, e.g.